Be sure to make it to La Boqueria in Barcelona - it's a huge food market on Las Ramblas - you can get a hefty portion of meat for 5 euros, an equally large thing of cheese for 5 euros, get a baguette for about a euro, and chow down. It's enough food for two hungry people. There are a lot of other snacks and a few tapas-esque places to eat at inside the market, all priced very reasonably, and it's worth a trip to check it out even if you don't get anything.